1. Field of the Invention
The present invention relates to a semiconductor device suitably used for a case in which semiconductor elements that generate much heat power are mounted, and a method for manufacturing the semiconductor device.
2. Description of Related Art
With the recent trend toward multifunction and reduction in size and thickness of electronic equipment, the semiconductor devices have become smaller and thinner, and the number of terminals tends to increase. For coping with this tendency, a so-called BGA (Ball Grid Array) package has been used. Unlike a conventional QFP (Quad Flat Package), a BGA package does not have an external lead protruding in the lateral direction. Instead, the BGA package has solder balls that are arranged in a matrix on the lower surface of a substrate and that serve as external electrodes for an electric connection with a mother board.
Since it is expected that semiconductor elements generating much heat are mounted on such a BGA package, heat diffusion is taken into consideration in the designing (see JP H08-139223 A for example).
FIG. 17 is a cross-sectional view showing a configuration of a conventional semiconductor device 101. FIG. 18 is a perspective view showing a thermal conductor 119 of the semiconductor device 101 in FIG. 17. Wiring patterns 112 are formed on the both surfaces of a substrate 113 made of an insulating resin, and the wiring patterns 112 are connected electrically to each other through via holes 117. A semiconductor element 111 is mounted on one principal surface of the substrate 113 through an adhesive 114 and connected electrically to the wiring pattern 112 on the substrate 113 through metal thin wires 115.
The thermal conductor 119 is made of a material having a preferable thermal conductivity such as Cu, Cu alloy, Al, Al alloy and Fe—Ni alloy, and it covers the surface of the substrate 113 on which the semiconductor element is mounted (semiconductor-element-mounting surface). The thermal conductor 119 has a contact portion 122 that is in contact with the substrate 113, an inclined portion 121 formed with an inclination from the contact portion 122, and a flat portion 120 formed continuously from the inclined portion 121 and to be parallel to the substrate 113. As shown in FIG. 18, a plurality of openings 131 are formed on the contact portion 122 and on the inclined portion 121. In FIG. 17, a sealing resin 116 is filled in the spacing between the thermal conductor 119 and the substrate 113 so as to seal the semiconductor-element-mounting surface of the substrate 113, the semiconductor element 111, the adhesive 114, and the metal thin wires 115 integrally. Ball electrodes 118 are arranged in a matrix on one of the wiring patterns 112 of the substrate 113 opposite to the semiconductor-element-mounting surface.
The semiconductor device 101 is configured so that heat generated by the semiconductor element 111 is diffused through the via holes 117 and the ball electrodes 118, and furthermore, the heat is diffused also from the semiconductor-element-mounting surface of the substrate 113 through the thermal conductor 119, and thus the semiconductor device 101 has excellent heat diffusion.
Furthermore, by providing a heat sink or the like (not shown) on an upper surface of the thermal conductor 119, namely, a part at which the sealing resin 116 is not formed, the effect of heat diffusion from the semiconductor-element-mounting surface can be enhanced further.
Next, a method for manufacturing the conventional semiconductor device 101 will be described below. FIGS. 19A-19F are cross-sectional views showing a process of manufacturing the semiconductor device 101. First, as shown in FIG. 19A, a substrate 113 with wiring patterns 112 formed on both surfaces thereof is prepared, and the adhesive 114 is applied on predetermined positions of the semiconductor-element-mounting surface of the substrate 113. Next, as shown in FIG. 19B, the semiconductor element 111 is placed on the adhesive 114 and adhered securely. Next, as shown in FIG. 19C, an electrode (not shown) of the semiconductor element 111 mounted on the substrate 113 and the wiring pattern 112 formed on the upper surface of the substrate 113 are connected electrically to each other through the metal thin wires 115. Next, as shown in FIG. 19D, the thermal conductor 119 is brought into contact with the substrate 113 so as to cover the semiconductor element 111.
Next, as shown in FIG. 19E, the substrate 113 in contact with the thermal conductor 119 is set on a lower mold 133 of a sealing mold 134, and sealed securely with an upper mold 132 of the sealing mold 134. At this time, the lower surface of the upper mold 132 of the sealing mold 134 and the upper surface of the thermal conductor 119 are in contact with each other. In this state, a sealing resin 116 is injected in an injection direction 136 from an injection gate 135 formed horizontally in the upper mold 132 of the sealing mold 134. As a result, through the openings 131 of the thermal conductor 119 as shown in FIG. 18, the sealing resin 116 enters the space between the thermal conductor 119 and the substrate 113. At that time, in the vicinity of the injection gate 135, the sealing resin 116 is on the upper surface of the thermal conductor 119. After curing the sealing resin 116, the upper mold 132 and the lower mold 133 of the sealing mold 134 are disengaged. Finally, as shown in FIG. 19F, the ball electrodes 118 are formed by attaching solder balls to external pad electrodes of the wiring pattern 112 formed on a surface of the substrate 113 opposite to the semiconductor-element-mounting surface, thereby configuring external terminals. In this manner, the semiconductor device 101 can be manufactured.
The conventional semiconductor device 101 can diffuse heat since the upper surface of the thermal conductor 119 is exposed from the sealing resin 116. However, since in the resin-sealing step, the resin is injected from the injection gate 135 provided at the sealing mold 134 (hereinafter, this method is referred to as a side gate method), the metal thin wires 115 will be deformed easily due to the resin injection.
Here, the deformation of the metal thin wires during the resin-sealing step in the side gate method will be described in detail with reference to FIGS. 20A-20C. FIGS. 20A-20C show a typical BGA, from which a thermal conductor is omitted for clearly showing the phenomenon.
FIG. 20A is a cross-sectional view showing a state just before a resin-sealing in the side gate method, and that corresponds to the cross-section taken along the line J-J′ in FIG. 20B and FIG. 20C. FIG. 20B is a top view showing the appearance of the metal thin wires 115 before resin injection, and FIG. 20C is a top view showing the appearance of the metal thin wires 115 and a flowing pattern of the resin after the resin injection.
As shown in FIG. 20C, the resin injected from the injection gate 135 in a direction 136 moves forwards while forming ripples centering on the injection gate 135. Here, each of dotted lines 137 indicates a position the resin reaches at a point of time.
The deformation level of the metal thin wires 115 has a relationship to “resin viscosity”, “resin current speed”, “angle of the tip of the flowing resin with respect to the metal thin wires” and the like. As shown in FIG. 20B, the metal thin wires 115 are arranged radially from the center of the semiconductor element 111. Therefore, as shown in FIG. 20C, after the resin injection is finished, some of the metal thin wires that are located in the vicinity of the injection gate 135 or at the side diagonally opposite to the injection gate 135 and thus not angled substantially with respect to the flowing direction of the resin are not deformed substantially. However, the remaining metal thin wires 115 are deformed depending on “resin current speed”, “angle of the tip of the flowing resin with respect to the metal thin wires”, and the like.
As a result, in a case of resin-sealing of the conventional side gate method carried out for a semiconductor device with metal thin wires 115 arranged across at a high density in accordance with the demand for smaller device and increase in the number of terminals, problems such as a short circuit may be caused by deformation of the metal thin wires 115 when the adjacent metal thin wires 115 are arranged at a narrow pitch.
Moreover, when the thermal conductor 119 as shown in FIG. 18 is included, the flow of the sealing resin is complicated and the fluidity deteriorates. This may cause a problem of imperfect filling of the sealing resin as well as the problem of deformation of the metal thin wires.